Modern papermaking machines and similar continuous process apparatus require industrial textiles to convey and dewater the filtrate through each section of the machine. Such textiles include, for example, forming fabrics, press felts and dryer fabrics; other similar fabrics are known and used. These textiles may be quite wide, up to 400 inches (10 m) or more, and are generally flat woven (although so-called endless woven fabrics are used as well), and are seamed so as to render them endless. A variety of seam types are known, including those which are more or less invisibly woven into the fabric so that the seam area does not present a discontinuity of fabric properties to the filtrate being conveyed. Such seams are referred to as woven seams and are commonly used in forming fabrics, which are designed to convey and support the papermaking fibers as the embryonic web is consolidated by drainage of fluid from the initially very dilute stock slurry which has been deposited onto the fabric.
The embryonic web is prone to marking and it is thus important that the seam present a uniform surface which is as similar as possible to the woven fabric structure. Therefore, a woven seam is preferred over other seam types for forming fabric applications because it provides less of a discontinuity in fabric properties. Other seam types, such as pin seams, coil seams and the like may be appropriate for use in press felts and dryer fabrics which are less prone to sheet marking. In order to weave the ends of a flat woven fabric together to form a woven seam, weft or cross-machine direction (CD) oriented yarns are removed from each fabric end in a process called “unraveling” to expose a fringe of warp or machine direction (MD) oriented yarns. The fringes are then overlaid, trimmed as necessary and the warp yarns rewoven with the weft yarns to form the seam. Automated seaming machines are often used for this purpose.
It will be appreciated that preparing the fringes of a papermaker's forming fabric for automated seaming can be a lengthy and laborious process requiring a high degree of skill and experience, particularly as these fabrics can be very finely woven, multilayer structures employing yarns whose diameters are in the range of from about 0.12 mm up to about 0.75 mm or more. Recently, automated means have become available which speed up the fringing process and reduce the amount of manual labor required.
In the unraveling process to prepare a fabric for seaming, short sections of the component weft yarns are cut, either by manual or automated means, and the cut yarn sections are then pulled out of the fabric. Care must be taken because, if the length of the sections of the cut weft yarns is too long, or the force used to pull them out is too great, the underlying warp threads can be damaged, resulting in discontinuities in the eventual seam. In addition, any crimp imparted to the yarns during the weaving process may be destroyed, making it difficult if not impossible to create a uniform woven seam.
Known apparatus for preparing a textile fringe for seaming use a hooked needle which penetrates the fabric from one side at a pre-selected distance from the end of the weft thread to be removed, and pulls the weft thread or threads that hook onto the needle out of the fabric on the needle's return stroke. The pulled out weft thread sections are then cut away. The disadvantage with such devices is that, each time the tip of the needle pierces the fabric, warp ends which are in close proximity to the piercing needle can be damaged or cut by the needle. In addition, each time the needle pierces the textile, there is a risk that the needle will split or cut warp yarns. Because the needle may pierce the fabric as many as 140 times for each inch of textile width (55 times/cm) and each quarter inch (0.64 cm) of weft threads pulled out, the risk of damage or breakage to the warp yarns when preparing a 30 foot (9.1 m) wide fabric for example occurs 200,000 times for every inch (2.54 cm) of fabric that is unraveled.
U.S. Pat. No. 4,736,499 to Köpcke (the '499 patent) discloses a device for automating the unraveling process to provide a fabric fringe suitable for spiral seaming. Spiral seaming involves the insertion of a plastic spiral into a narrow fringed channel across the width of the two fabric ends that are to be joined. In the device according to the '499 patent, an unraveling unit uses a plurality of vertically reciprocating needles in combination with a cutter to pull out and cut sections of weft thread. The unit travels across the width of the fabric unraveling a number of yarns corresponding to the number of needles in the unraveling unit.
This can be disadvantageous in certain instances because, if a wider fringe is required, then the unit must be repositioned and the unraveling process repeated across the entire width of the fabric. Although a narrow fringe of from two to ten threads in width is sufficient for spiral seaming, a woven seam such as would be used in a papermaker's forming fabric requires a larger fringe of from about 1 inch (2.54 cm) to about 10 inches (25.4 cm) in width. This will require the removal of hundreds of weft threads and numerous passes of the device. A second deficiency of this fringing device is that it employs a mechanical sensor to follow the channel between two adjacent weft threads and ensure straight tracking of the unraveling unit. This sensor may not track properly across fabrics with tight or multilayered weaves. A third deficiency is that the device uses a trailing cutter to cut the pulled threads after they have been released by the needles; such a cutter may not function adequately on soft-fibered fabrics, as soft threads may not be stiff enough to maintain their position as the cutter moves into them. Thus, the device disclosed in the '499 patent may not be suitable for applications other than preparing fabrics for spiral seaming.
U.S. Pat. No. 6,014,797 to Kuster et al. (the '797 patent) discloses another device for automatically unraveling a fringe area in a fabric. This device uses a reciprocating, hooked needle and a reciprocating blade to pierce the fabric, pull one or more interwoven weft yarn tails out of the woven fabric structure, and then cut the tails off when they are displaced from the fabric plane. The needle and hook are advanced in the parallel direction to the longitudinal warp yarns, unraveling the weft yarns until a fringe area of a desired width has been formed. The apparatus is then moved laterally along the edge of the fabric to the next unraveling location and the cycle is repeated until the fringe area extends to the desired width along the length of the fabric edge.
A disadvantage of this device is that, each time the needle pierces the fabric, there is a potential to damage or even break warp threads that are in close proximity to the needle. Because the needle need to be pulled out of the plane of the textile to give space for the cutter to cut the pulled out yarn tails. Damage to the remaining MD yarns may occur after each time the needle pierce the fabric again. An additional disadvantage is that the thread(s) hooked into the needle may slide and break.
Thus, it would be desirable if a method and apparatus were available which provided reliable capture of the fringe yarns with reduced risk of breakage and which was adjustable to fringe a desired width of fabric in preparation for a seaming process. It would be particularly desirable if such a method and apparatus could be used in multilayer fabrics which are woven at high yarn density, without causing damage to any of the component yarns used in seam formation.
The present invention seeks to provide a novel method and apparatus for the automated and reliable unraveling of one or multiple weft threads in a woven industrial textile such as a papermaker's fabric. The apparatus creates a longitudinal MD oriented channel in the fabric in which all of the CD oriented yarns have been removed and all of the MD yarns are left undamaged and available for use in seam formation. In addition, the method and apparatus of this invention provides for the automated unraveling of yarns in a multilayer woven fabric, which fabric is woven at a yarn density of about 180 yarns per inch or more. Further, the method and apparatus of this invention are able to remove yarns having both circular and non-circular cross sectional shape.
The method and apparatus of this invention are suitable for use in a variety of industrial textiles, including papermaker's fabric and similar filtration and separation fabrics which require a seam.